Biology subjects

Tessmer, K.

Publications and source records attributed to Tessmer, K..

5 recordsLinked to original sources

bioRxiv2026

Transplanted human photoreceptors differentially survive, incorporate, and mature in mildly and severely degenerated mouse retinae

Photoreceptor transplantation is considered a disease-agnostic therapeutic strategy for retinal degenerative diseases with highly heterogenous genetic, molecular, and cellular pathologies. While integration of human photoreceptors enriched from stem cell-derived retinal organoids was noted in previous preclinical studies, the potential influence of retinal degeneration severity on transplantation efficiency has not been systematically assessed. Here, we employed mice presenting mild or severe retinal degeneration as recipients for human induced pluripotent stem cell-derived photoreceptors. Donor cells formed multi-cellular clusters that structurally integrated from 3 weeks post-transplantation (wpt) in mildly degenerated retinas, closely interacting with host Muller glia, resulting in proper maturation characterized by inner/outer segment and synapse formation by 26 wpt. In contrast, in severely degenerated hosts, donor photoreceptors remained mainly singularized and scattered in the subretinal space, showing limited structural integration or signs of maturation. Differential maturation of donor cells in mild vs. severe hosts was confirmed by single-cell RNA-sequencing analysis. However, transplantation at the beginning of the degeneration process of the severe model allowed structural integration and maturation of donor photoreceptors, despite complete loss of endogenous photoreceptors over time. The study thus shows that survival, integration, and maturation of donor photoreceptors depend on the degenerative retinal microenvironment shaping significantly transplantation efficiency.

neuroscience↗

bioRxiv2024

Extensive monolayer formation depends on a subpopulation of transplanted human iPSC-derived RPE cells

Loss of the retinal pigment epithelium (RPE) in the eye leads to photoreceptor dysfunction and death causing eventually vision loss. Cell replacement strategies using RPE cells derived in vitro from pluripotent stem cells (PSCs) are currently evaluated as a potential therapeutic strategy. Generation of polarized monolayers represents an essential prerequisite for proper RPE function, however, monolayer formation following transplantation of RPE cell suspensions has not been systematically assessed. Using the sodium iodate mouse model of acute RPE depletion, significant increase in monolayer formation capacity of passage (P) 1 vs. P2 human iPSC-derived RPE cells was observed three weeks after transplantation. Transplant-derived monolayers showed characteristic apicobasal polarity, RPE marker expression, phagocytosis function, and preservation of the host outer nuclear layer. The cell surface marker panel CD54+/PSA-NCAM- was identified to enrich for an RPE subpopulation with high potential for monolayer formation following transplantation. Results underline the importance of defining and isolating competent cell subpopulations for successful RPE transplantation.

neuroscience↗

bioRxiv2021

Extensive incorporation, polarisation and improved maturation of transplanted human cones in a murine cone degeneration model

Once human photoreceptors die, they do not regenerate, thus photoreceptor transplantation has emerged as a potential treatment approach for blinding diseases. Improvements in transplant organization, donor cell maturation and synaptic connectivity to the host will be critical in advancing this technology to clinical practice. Unlike the unstructured grafts of prior cell suspension transplantations into end-stage degeneration models, we describe extensive incorporation of iPSC retinal organoid-derived human photoreceptors into mice with cone dysfunction. This incorporative phenotype was validated in both cone-only as well as pan-photoreceptor transplantations. Rather than forming a glial barrier, Muller cells extend throughout the graft, even forming a common outer limiting membrane. Donor-host interaction appears to promote polarisation as well as development of morphological features critical for light detection, namely formation of inner and well stacked outer segments oriented towards the RPE. Putative synapse formation and graft function is evident both at a structural and electrophysiological level. Overall, these results show that human photoreceptors interact readily with a partially degenerated retina. Moreover, incorporation into the host retina appears to be beneficial to graft maturation, polarisation and function. HighlightsO_LIGeneration of the first human iPSC cone reporter line C_LIO_LIHuman cones extensively incorporate into the retina of mice with cone degeneration C_LIO_LIDonor cone age and time in vivo are important factors for transplant incorporation C_LIO_LIIncorporation into the host retina correlates with graft polarisation C_LIO_LIImproved photoreceptor maturation after transplantation in vivo vs. in vitro C_LIO_LIRe-establishment of cone-mediated light-responses in the cone deficient mouse C_LI

neuroscience↗

bioRxiv2021

Label-free imaging flow cytometry: analysis and sorting of enzymatically dissociated tissues

Biomedical research often relies on identification and isolation of specific cell types using molecular biomarkers and sorting methods such as fluorescence or magnetic activated cell sorting. Labelling processes potentially alter the cells properties and should be avoided, especially when purifying cells for clinical applications. A promising alternative is the label-free identification of cells based on their physical properties. Sorting real-time deformability and fluorescence cytometry (soRT-FDC) is a microfluidic technique for label-free analysis and sorting of single cells. In soRT-FDC, bright-field images of cells are analyzed by a deep neural net (DNN) to obtain a sorting decision, but sorting was so far only demonstrated for blood cells which show clear morphological differences and are naturally in suspension. Most cells, however, grow in tissues, requiring dissociation before cell sorting which is associated with additional challenges including survival, changes in morphology, or presence of aggregates. Here, we introduce methods for robust analysis and sorting of single cells from mammalian nervous tissue and provide DNNs which are capable of distinguishing visually similar cells. Exemplarily, we employ the DNN for image-based sorting to enrich photoreceptor cells from dissociated retina for transplantation into the mouse eye. Results provide evidence that the combination of machine learning and soRT-FDC allows label-free enrichment of target cells from dissociated tissues.

biophysics↗

bioRxiv2019

Biological Plasticity Rescues Target Activity in CRISPR Knockouts

Gene knockouts (KOs) are efficiently engineered through CRISPR-Cas9-induced frameshift mutations. While DNA editing efficiency is readily verified by DNA sequencing, a systematic understanding of the efficiency of protein elimination has been lacking. Here, we devised an experimental strategy combining RNA-seq and triple-stage mass spectrometry (SPS-MS3) to characterize 193 genetically verified deletions targeting 136 distinct genes generated by CRISPR-induced frameshifts in HAP1 cells. We observed residual protein expression for about one third of the quantified targets, at variable levels from low to original, and identified two causal mechanisms, translation reinitiation leading to N-terminally truncated target proteins, or skipping of the edited exon leading to protein isoforms with internal sequence deletions. Detailed analysis of three truncated targets, BRD4, DNMT1 and NGLY1, revealed partial preservation of protein function. Our results imply that systematic characterization of residual protein expression or function in CRISPR-Cas9 generated KO lines is necessary for phenotype interpretation.

bioengineering↗